FLAGSTAFF, Ariz. -- Crews fighting a wildfire in a northern Arizona canyon focused Monday on building containment lines along the last unprotected stretch of the blaze.

Firefighters will build 3 miles of protection lines on the southern end of the Slide Fire after having completed much of their work on the blaze's key northern and western flanks.

The human-caused fire has been burning since Tuesday around Oak Creek Canyon, a scenic recreation area along the highway between Sedona and Flagstaff that would normally be crowded with tourists Memorial Day weekend.

No homes have been destroyed.

The fire covered more than 25 square miles and was 25 percent contained by Monday morning.

It had grown more than 3 square miles since the latest report on its size.